Adjustable precision electrical resistor



INVENTORS. CHARLES L. WELLARD BY WALTER H. DOUGLASSISR ATTORNEY.

United States Patent M 3,475,714 ADJUSTABLE PRECISION ELECTRICAL RESHSTOR Charles L. Wellard, King of Prussia, and Walter H. Douglass, Sn, Oreland, Pa., assiguors to American Components Incorporated, Conshohoeken, Pa.

Filed Feb. 13, 1968, Ser. No. 705,052 Int. Cl. HOlc J/02 US. Cl. 338-273 8 Claims ABSTRACT OF THE DISlILOSURE The present device provides for slidably mounting a standard miniaturized electrical resistor within an electrically non-conducting housing. Further disposed in said housing is a resilient, electrically-conducting member, said member being circumferentially in electrical contact with the conducting surface of said standard miniaturized resistor. The standard resistor is moved to the proper location with respect to the resilient member to provide a desired resistance value between the end of the standard resistor and the resilient member. Thereafter the standard resistor can be permanently, physically fixed thereby permanently fixing the resistance value.

This invention relates to a precision electrical resistor whose value can be adjusted and then fixed.

BACKGROUND Small potentiometers and small variable resistors are in great demand in the present state of the electronic component art. In the past this kind of device usually included a housing means, generally of cylindrical shape, within which there had been disposed electrically resistant material. Normally a conducting wiper was arranged to be passed over the electrically resistance material. In some of the prior art devices, the electrically resistant material is secured to the inner surface of the cylinder and a suitable electrical connection is made to at least one end of this electrically resistant material. With this kind of a device there has been provided a shaft upon which a block member can be moved, either in response to a rotating threaded element with which it is engaged, or simply, by inserting a screwdriver or other instrument and pushing the block member.

The block member usually has one or more wipers made of electrically conducting material which are mounted to come in contact with said electrically resistant material secured to the inner surface of the cylinder. The wiper or wipers are further connected to an electrically shorted return line or bar. In some of these devices the electrically shorted return line comprises a second shaft upon which a second wiper block is located, or in some embodiments it is simply the shaft upon which the first block is mounted.

This prior art wiper-block type of variable resistor presents a number of disadvantages when considered with respect to vary small components and/ or components which are subjected to vibrating modes of operation such as being used in an aircraft or a space vehicle.

The Wiper-block on a shaft arrangement as an adjustable resistor necessitates, by its very design, a rather complicated mechanical device because somehow the wiper-block must be inserted and movably mounted within the housing means. Such a fabrication is sometimes accomplished by having the housing means made up of two sections which fit over the shaft and the block. Other times the fabrication is accomplished by placing the block on the shaft and then providing an end cap after the block and the shaft have been located within a one-piece housing means. In each instance the housing means has the 3,475,714 Patented Oct. 28, 1969 resistant material therein. In these last modes of operation there still must be provided some further means for connecting the end of the shaft to the electrical conducting means so that the wiper may have electrical continuity.

With respect to vibration it becomes obvious that if the block has been threaded and the shaft has been threaded (or if they are slidably engaged) the block is apt to move in response to some vibration which would of course nullify the original purpose of the device; namely to set the resistor at some carefully selected resistance value.

In some versions of prior art adjustable resistors there have been provided schemes whereby the resistance wire is simply U-shaped in form and there is a shorting element in contact with two legs of the resistance wire, the shorting element being mounted on a block of non-conducting material. The block has threads therein and is threadably engaged with a bolt or threaded shaft. As the threaded shaft is rotated, the block is moved forward and backwards similar to a lathe operation. The shorting element of course provides the point at which the resistance of one leg of the wire is added to the resistance of the other leg of the wire to provide the resistance value being sought. This kind of a device also requires a complicated mechanical assembly procedure by the very nature of its design. It has the same disadvantage that the wiper block has in that if there is vibration the bolt or threaded shaft is apt to move and hence move the shorted element to a new position, thereby nullifying the purpose of the device.

In another kind of prior art device a fiat resistance element has been housed in housing means having two halves. Encapsulating this housing means is a cylinder device with a spiral shape head or ridge formed therein. When the cylinder is rotated the position of the ridge changes on the upper edge of the flat resistor and hence provides a different location as it is rotated. The resistor is provided with an end terminal and a further wiper connection to the rotating cylinder. Accordingly, the position of the bead contact is changed and the value of the resistance changes. This particular kind of a device is even more complicated to assemble and fabricate than the previously mentioned devices and hence there is great difliculty in trying to fabricate such a device as a small element for a miniaturized component. In addition it has the disadvantage that in response the vibrations the cylinder itself rotates and changes the bead location thereby changing the resistance value and defeating the purpose of the device itself.

Finally (although there are probably others), the prior art has provided a straightforward wire wound potentiometer type device with two wipers mounted in a circular position. The two wipers are simply moved clockwise or counter-clockwise as the case may be to new positions thereby providing a change in resistance value. This kind of device does not lend itself to the physical configuration of a resistor of the kind used in data processing circuitry or television circuitry and it is also subject to change of position in response to vibration.

SUMMARY The present device provides an electrically non-conducting housing with a cylindrically shaped aperture therein. Within the cylinder shaped aperture there is located a standard miniaturized resistor. The normal leads of the resistor are disposed to pass through holes at the respective ends of the cylindrical aperture. In addition at one end of the cylindrical aperture there is a terminal element which has a hole therethrough to accept one of the normal resistor leads. This terminal element is permanently fixed to the housing means and is used to permanently fix the location of the resistor within the housing means after a proper resistance value has been attained by locating the resistor.

Finally the housing means itself is made up of two parts which lock together in a tongue-in-groove fashion. Located at the positions where the surfaces of the two separate parts of the housing come together is a resilient electrically conducting terminal-clip that slips over the standard resistor element and provides a contact therewith completely around the surface of the element. This electrically conducting terminal-clip protrudes from the housing means to serve as an electrical connection.

The aperture provided in the housing means is sufficiently large that the standard resistor can be moved therein, so that each of its capped ends can come in contact with the electrically conducting terminal-clip. Accordingly, once the housing has been assembled with the resistor therein and the clip mounted, the resistor is moved to the loaction which will provide the proper resistance value between the normal resistor lead end and the terminal-clip. When so located, the normal lead protruding from a permanent terminal element is soldered thereto or crimped therewith. Thereafter the normal lead end can be cut off. The standard resistor is no longer able to move within the housing even in response to vibration and the permanent terminal element provides a good connection for the resistor lead to other circuitry with which the component is used.

The features and objetcs of the present invention will be better understood with a study of the following description and the drawings in which:

FIGURE 1 is a pictorial schematic drawing of the terminal clip;

FIGURE 2 is a pictorial schematic drawing of the terminal clip being slipped over a standard resistor;

FIGURE 3 is a front view of the terminal clip located on a standard resistor (with the standard resistor sectionalized) FIGURE 4 is a pictorial schematic of the housing means;

FIGURE 5 is an exploded side view of the housing means and a standard resistor with a terminal clip thereon;

FIGURE 6 is a breakaway view of a housing with a standard resistor therein and located toward one end thereof;

FIGURE 7 is a pictorial view of the permanent terminal;

FIGURE 8 is a breakaway view of a housing with a standard resistor therein and located toward the other end.

The trend in the electronic art has been, and is, to devise smaller and more compact circuits which necessitate smaller and more compact components. The example of the dramatic reduction of tube circuits to transistor circuits and then finally to integrated circuits is a typical illustration of the aforementioned trend. The miniaturization is not without a price, in design effort as well as criticality and reliability. The more components that are crammed into a given sapce, the more these components must be able to function under high temperature condi tions. The foregoing is axiomatic since most of the components generate some heat. In addition it is self-evident that the circuits and the components must include fewer and smaller elements per se.

The present invention employs simplicity of design to provide a fully adjustable resistor which can be extremely small and which is as reliable as the precision standard resistor empolyed in its fabrication.

Consider FIGURE 1 which is a connector clip and whose role in the complete assembly will become apparent hereinafter. The connector clip of FIGURE 1 (which is the preferred embodiment) has a connector stem 11 which extends from the housing of the variable resistor assembly and which is so formed that a lead wire to other circuitry may be connected through the eye 13. In the preferred embodiment the connector clip is made of a blue steel spring stock, but it should be understood that this connector clip can be made of any resilient metal which can act as a good electrical conductor.

The connector clip is formed so that it can be stamped from a single piece of metal. By forming the connector clip as above described (i.e., so that it can be stamped from a single piece of metal) it provides for an economic fabrication of the adjustable resistor device. However, it should be understood that the connector clip can be formed with some resilient metal, or conductive material, without having it stamped from a single piece and still be within the spirit of the present invention. Preferably the connector clip should be a unitary piece for easy assembly because easy assembly is a large factor in reducing the cost of the overall fabrication of the adjustable resistor device.

In FIGURE 1 it will be noted that the connector clip is formed with a pedestal section 17 from which the connector stem 11 extends. The pedestal section 17 is further formed to have an arch-like groove 19 cut therefrom and further an aperture 21 cut from the two peninsulae formed by the arch-like groove 19. The ends of the aperture 21 are formed into two grooves 23 and 25 which result in the two peninsulae sections being formed into two wraparound legs, respectively 27 and 29. The legs 27 and 29 are identified as wraparound legs because as will become apparent these legs when properly assembled with a standard resistor actually wrap around the resistor and provide an electrical contact between the outer surface of the standard resistor and the inside surface of the aperture 21. The wraparound legs 27 and 29 can be pivoted at the points 31 and 32, respectively, i a direction out of and into the patent drawing, so that the peninsulae sections actually become further separated. In other words the groove 25 can be angularly enlarged. This is dramatically shown in FIGURE 2. At the same time the wraparound legs 27 and 29 can be pivoted toward the outer sides of the terminal clip. This last mentioned movement would be in a direction that would tend to close the groove 19. This movement of course enables the wraparound legs to be initially opened up when they are fitted onto the standard resistor and yet to spring back due to the resiliency of their material to form a firm electrical contact (circumferentially) with the conducting surface of the standard electrical resistor.

- When we consider FIGURE 2 we find the terminal clip 15 being assembled with the standard type resistor 33. It will be noted in FIGURE 2 that the wraparound legs 27 and 29 have been split and pivoted in a sense, out of the drawing and into the drawing (the drawing in this instance meaning the patent drawing). This maneuver is a simple matter for the person assembling the terminal clip onto the resistor. In a further action the terminal clip is pushed downward so that the aperture 21 is filled by the conducting surface 35 of the resistor 33. When the terminal clip has been pushed down so that the aperture 21 is filled by the conducting surface 35 of the standard resistor, that is, when the wraparound legs 27 and 29 completely encompass or wrap around the conducting surface 35, the terminal clip 15 will of its own accord, or with the help of the person making the assembly, become perpendicular to the resistor so that only its side edge would be seen from the position shown in FIGURE 2. The front view of this last described position is shown in FIGURE 3.

In FIGURE 3 the connector clip 15 is shown in a completed assembly position, i.e., around the conducting surface 35. Actually in FIGURE 3 the diagram is shown with the end cap 39 and the lead wire '41 of FIGURE 2 removed. In FIGURE 3 the wraparound legs 27 and 29 are shown in contact with the conducting surface 35 and the conducting surface 35 is shown secured to a substrate 37.

Returning momentarily to FIGURE 2 it is to be understood that the resistor 33 is a standard type resistor of the kind used in data processing equipment, television sets,

radio equipment, and the like. In this particular embodiment there is shown a resistor having a thin conducting film 35 on a substrate 37 with two end caps 39 and 40. In addition there are two lead wires 41 and 42 connected to the end caps. Within the spirit of the present invention, the resistor might be a wire wound resistor instead of a thin film type resistor or further might be the kind of resistor where the electrically resistant material is impregnated into a non-conducting base but which has an outer layer of material that is conductive.

After the connector clip has been assembled onto the conducting surface 35 of the standard resistor 33, the resistor 33 is mounted in the housing 43 shown in FIGURE 4. In FIGURE 4 there is shown a two section housing 43. The two section housing 43 is composed of a tongue section 45 and a grooved section 47. In the tongue section 45 there is an aperture 49 formed. The aperture 49 is larger than the caps 39 and 40 and must be formed to accommodate whatever resistor is contemplated for use in the housing. The aperture 49 is made sufiiciently larger than the caps 39 and 40 so that the resistor 33 can be readily moved (axially) within the aperture. As shown by the dashed line in FIGURE 4, the aperture 49 runs almost completely through the tongue section 45. In the end wall 51 of the tongue section 45 there is a hole out which is smaller than the aperture 49 but which is sufi'iciently large to allow the permanent terminal 53 to pass therethrough.

In the preferred embodiment, the housing 43 is made up of suitable plastic material which can be readily molded. However, it should be understood that the housing 43 can be made of any non-conducting material and it need not take the rectangular or squared-off shape shown in FIGURE 4. The housing assembly preferably should be made in sections and should have an aperture therein which is large enough to permit the movement of a resistor. With the aperture 49 being formed in the tongue section 45, the permanent terminal assembly is simply inserted into the aperture 49 and passed through the hole in the end wall 51. The permanent terminal assembly has a flange on the end thereof, which is larger than the portion extending from the housing and which is as large as the aperture 49. When the permanent terminal is inserted into the aperture 49 the flange section comes to rest against the end wall 51, thereby perma nently positioning the terminal in the tongue section. It should be understood that the permanent terminal could be similarly assembled into groove section 47 or there could be a permanent terminal on each of the sections 45 and 47. In the permanent terminal assembly there is a groove 56 into which molten plastic runs during fabrication. When the molten plastic hardens the permanent terminal is securely fixed.

With the permanent terminal assembly having been located in the tongue section 45, the person fabricating the assembly simply loads the standard resistor 33 (with the connector clip mounted) into the aperture 49 and then fits the grooved section 47 into place against the tongue section 45. It will be noted in FIGURE 4 that the grooved section 47 also has an aperture 50. The aperture 50 is the same size as the aperture 49 and fits over the end caps 40 of the resistor 33. In the end wall 55 of the grooved section 47 there is formed a hole 57 which is sufficiently large to permit lead wire 42 to pass therethrough. It becomes evident that when the grooved section 47 is fitted with the tongue section 45 the right-hand half of the resistor 33 may be housed in the aperture 50.

A disposition of the resistor with the apertures is shown in FIGURE 5. In FIGURE 5 it becomes apparent that when the groove section 47 is assembled with the tongued section 45, the resistor 33 will be encapsulated, or housed, within the combination apertures 49 and 50. It also is apparent from FIGURE 5 that the terminal clip 15 will extend from the housing when it is fully assembled, thereby permitting other circuitry to be connected thereto for further use.

In FIGURE 6 the housing 43 is shown completely assembled and a portion is cut away therefrom to show the position of the resistor 33. In the embodiment shown in FIGURE 6, the resistor 33 has been pulled to the extreme left-hand side. This movement is efiFected by simply pulling on the lead wire 41. When the resistor 33 is pulled to its extrememost left-hand side there is an electrical circuit between the lead wire 41 through the resistor 33 and through the terminal clip 15. In this particular situation the full value of the resistor 33 can be realized between the wires 41 and the terminal clip 15. If for some reason or other the user should want to use the full value of the resistor 33 in this kind of an arrangement the resistor 33 would be pulled to its extreme-most left-hand side. Actually such a use is highly unlikely because if the resistor were to be used at its full value the resistor 33 could simply be used without housing it in the housing means 43. In a variable or adjustable resistor of this kind, the resistor is usually used in some position between the most extreme left-hand side and the most extreme right-hand side, i.e., it is used at a position where some lesser value of resistance is realized between lead wire 41 and the terminal clip 15. When the resistor 33 has been located in the proper location so that the resistance value between the lead-in wire 41 and the terminal clip 15 is the value necessary for the particular circuit (in which the variable resistor is used), the lead-in wire 41 is soldered, or conductively secured, to the permanent terminal 53. This is usually accomplished by providing a few drops of solder at the opening of the permanent terminal which solders the lead-in Wire 41 to the permanent terminal 53. Such a configuration is shown in FIGURE 7.

In FIGURE 7 there is shown the permanent terminal 53 out of the housing so that the flange 54 is better appreciated. The device of FIGURE 7 shows permanent terminal 53 with the lead wire 41 clipped oil and electrically secured thereto by a few drops of solder 59. The lead wire can be crimp'ted with the permanent terminal.

FIGURE 8 shows the housing assembly completely put together and with a resistor 33 moved completely to the right-hand side. When the resistor 33 is moved completely to the right-hand side the connector clip 15 is virtually abutting the end cap 39. This of course once again gives the full resistance value of the resistor 33 between the lead-in wire 42 and the terminal clip 15. In the alternative there would be a short circuit between leadin wire 41 and the connected clip 15. As stated before, it is highly unlikely that the device would be used in this right-handmost mode, since it would be a simpler matter to use the resistor 33 by itself. However, the configuration of FIGURE 8 is shown for the purpose of showing that the resistor 33 can be moved to the extreme righthand side. As indicated before, it is more likely that the resistor would be located at some position between that shown in FIGURE 6 and FIGURE 8. Again in connection with FIGURE 8 it should be noted that once the resistor is located in the proper position so that the resistance value which is required is attained, between lead-in wire 41 and terminal clip 15, both of the lead Wires 42 and 41 are cut off and the lead-in wire 41 is permanently secured to the permanent terminal 53.

Now as mentioned before there could be a permanent terminal on the end of the housing through which the lead-in wire 42 goes and the device could be used as a three terminal device.

The present variable or adjustable precision resistor has a number of advantages over the prior art. First of all, the assembly is quite simple and enables the person in the resistor factory who is assembling these adjustable resistors to rapidly fabricate the same or even to have the resistor assembled by machine. The wraparound arms 27 and 29 provide a complete electrical contact with the conducting surface so that there is virtually no ill elfects from current density. problems. Current density problems occur with wiper type variable resistors and hence these resistors are difiicult to calibrate and do not have the reliability of the present device. Thirdly, once the variable resistor has been fixed with the resistance value required, the resistance value is made permanent by soldering the lead-in wire 41 to the permanent terminal 53. Accordingly, the variable resistor is not subject to the change of value due to vibration and as discussed earlier, other variable resistors are subject to such changes. In this regard, it should be noted that vibration will not cause the resistor to open at the connector clip jointure. In other types of units if a force (shock) is applied perpendicular to the axis of the housing, the wiper will lift from the resistant material and open the resistor.

What is claimed is:

1. An adjustable resistor comprising:

a standard resistor element having first and second connector leads at the respective ends thereof and having an outer conducting surface;

electrically non-conducting housing means having a locating aperture holding said standard resistor therein and formed to permit said standard resistor to effeet a limited movement along the axis of said locating aperture;

connector clip means in substantially complete contact with said standard resistor along at least one segment of its circumference and mounted in said housing means to. effect said contact;

permanent terminal means secured to said housing and having said first connector lead therethrough; and

means securing said first connector to said permanent terminal means.

2. An adjustable resistor according to claim 1 wherein said standard resistor comprises a cylindrically shaped ceramic substrate coated with a thin film of electrically resistant material.

3. An adjustable resistor according to claim 1 wherein said housing means comprises a tongue'section and a grooved section, and wherein each of said sections has an aperture therein such that when said tongue section is fitted into said grooved section said last mentioned apertures acting together form said locating aperture.

4. An adjustable resistor according to claim 1 wherein said connector clip is formed to protrude from said housing means and further having means for electrical connection thereto.

5. An adjustable resistor according to claim 1 wherein said connector clip is formed of a resilient electricallyconducting material and is formed to separate into two sections at one end thereof to thereby be readily slipped over said standard resistor.

6. An adjustable resistor according to claim 1 wherein said connector clip has a pedestal section and a connector stern and wherein said pedestal section has two wraparound legs formed therein, said wraparound legs being formed to be slidably mounted and in substantially complete contact with said at least one segment of the circumference of said standard resistor.

7. An adjustable resistor according to claim 6 wherein said two wraparound legs are formed from two penninsula-shaped elements which together form an aperture to fit over said standard resistor.

8. An adjustable resistor according to claim 1 wherein there is further included electrical connector means protruding from the end of said locating aperture lying opposite from said permanent terminal means.

7/1955 Reid 338- 2,807,695 9/1957 Delmonte 338-150 2,870,304 l/l959 OBrian 338-150 LEWIS H. MYERS, Primary Examiner T. J. KOZMA, Assistant Examiner US. Cl. X.R. 338l50, 276, 332 

